Locking system on a cascade thrust reverser

ABSTRACT

The invention provides a locking system on a cascade thrust reverser for a bypass turbojet, the reverser ( 20 ) comprising guide means ( 60 ) for the movable parts ( 50 ), and the guide means ( 60 ) comprising rails ( 64 ) attached to the movable parts ( 50 ) and tracks ( 62 ) attached to the longitudinal members ( 36 ). 
     According to the invention, the locking system ( 80 ) comprises locks ( 82 ) located at the end ( 62   a ) of each track ( 62 ) in the opening direction ( 52 ), each lock comprising a bolt ( 110 ) capable of preventing the rail ( 64 ) moving in the opening direction ( 52 ).

The invention relates to thrust reversers of the cascade typesurrounding the bypass turbojets of airplanes, its reversers comprisinga fixed part and a movable part, and more specifically to a lockingsystem for immobilizing the movable part on the fixed part.

Thrust reversers are familiar devices that allow the flow of propulsiongases produced by the bypass turbojet to be temporarily deflectedforward. The reverser is in the general form of a body of revolutionsurrounding the turbojet and is basically concentric with it. Thereverser has a fixed part and at least one movable part. Schematically,the fixed part consists of a front frame and a rear frame, both annularin shape and connected by a plurality of longitudinal members in themanner of a squirrel cage. The front frame, the rear frame and thelongitudinal members are rigid and lightweight hollow structures whichgive the reverser its stiffness. The whole is surrounded by an externalcowling and an internal cowling. Between the longitudinal members areradial holes equipped with a plurality of small vanes which togetherform cascades, these vanes being capable of deflecting the cold flow ofthe bypass turbojet in the forward direction. The movable parttranslates forward or backward to either cover or expose the radialopenings. The movable parts are guided during their translation by railssliding in parallel tracks, the tracks being attached to thelongitudinal members. The movable parts are controlled by rams which areusually attached to the front frame.

The movable parts are held in the closed position by so-called “main”locks. These locks are usually situated on the front frame and catch thefront ends of the movable parts. The main locks can become inoperativefollowing rupture of a rotor or vane of the turbojet causing debris tobe thrown around the turbojet. Debris impacting the reverser can deformthe reverser and/or damage the locks. The danger then is that themovable parts may move into the open position, causing accidental andcatastrophic thrust reversal while the plane is in flight. To reducethis danger very substantially, secondary locks are fitted at differentlocations than the main locks, for example on the longitudinal members.But the risk of the reverser being deformed by simultaneous impact onthe main locks and secondary locks is not zero. This risk can beprevented by adding still more locks, but then there is a greater riskof a lock failing to open when the airplane pilot engages thrustreversal, in which case the thrust reverser would fail to operate.

The locks are usually of the hook type, that is the bolt is in the formof a hook and retains a roller on the end of a tie rod, the other end ofthe tie rod being connected to a movable part while the body of the lockis attached to the fixed structure. However, there are drawbacks withsuch locks:

-   -   They are of limited effectiveness in the event of impact,        because the roller can come out of the hook if the reverser is        deformed, or the hook or the tie rod may break.    -   These locks are large and become difficult to install if the        reverser is very thin, that is if the distance between the inner        cowling and the outer cowling is restricted.    -   At the points where they are attached, these locks generate        large torques and extra members have to be inserted to reinforce        the fixed structure and movable parts at these points, these        extra members having the drawback of increasing the weight and        cost of the reverser.

An initial problem to be solved is that of creating a locking system fora cascade thrust reverser, where the system must be insensitive both toimpact and to the accidental deformations of the reverser which mayarise from such impact.

A second problem to be solved is that of making the locking system smallso that it can be fitted between the walls of very thin reversers.

A third problem to be solved is that of creating a locking system for acascade thrust reverser that does not generate torque at the locationswhere they are attached to the reverser.

To solve the first problem, the invention provides a locking system on acascade thrust reverser for a bypass turbojet, the reverser comprising afixed part which in turn comprises a plurality of radial openingsseparated by longitudinal members, the radial openings being closed bymovable parts moving in the closing direction, the radial openings beingexposed when the movable parts move in the opening direction, thereverser comprising guide means for the movable parts, the guide meanscomprising rails attached to the movable parts and parallel tracksattached to the longitudinal members, and the rails sliding in thetracks, with preferably one degree of freedom in translation, the tracksthus forming elements of the fixed part and the rails elements of themovable parts.

Such a system is noteworthy in that it comprises locks attached to thefixed part in the vicinity of the end of each track in the openingdirection, each lock comprising a bolt positioned in line with thecorresponding track, the bolt being movable between a locked positionand an open position, the bolt in the locked position preventing therail moving in the opening direction when the rail is retracted in thetrack, and the bolt in the open position not preventing the rail frommoving in the opening direction.

With such an arrangement, the end of the track and the lock move in thespace in essentially the same manner when the fixed part deforms becausethe lock is in the vicinity of the end of the track. The bolt thereforeremains substantially in line with the track in the vicinity of its end,and no movement of the movable part in the opening direction is possibleas long as the bolt is in the closed position. This solves the firstproblem.

When it is in the closed position, the bolt has the effect ofimprisoning the rail in the track, these two parts being inherentlymechanically strong, which makes the locking system relativelyinsensitive to impact and solves the second problem. Notice that thisimprisoning of the rail in the track also has the advantage that themovable parts are restrained even in the event of major damage.

The third problem is solved by the fact that:

-   -   the lock generates only very limited torque at the point where        it is attached to the fixed structure, because it is close to        the end of the track,    -   the lock generates no torque on the rail, because it is in line        with the track and therefore with the rail.

A clearer understanding of the invention and its advantages will begained from a perusal of the following detailed description and of theappended figures.

FIG. 1 illustrates the general structure of a cascade thrust reverser,with the movable parts in the open position.

FIG. 2 illustrates in perspective an example of a locking systemaccording to the invention.

FIG. 3 illustrates the same locking system in plan view, with the lockin the open position.

FIG. 4 shows by a local section on A the disposition of the railretracted inside the track, the bolt being in the open position.

FIG. 5 shows by a local section on A the disposition of the rail comingout of the track, the bolt being again in the open position.

FIG. 6 illustrates by a plan view the same example but with the lock inthe closed position.

FIG. 7 shows by a view in local section the rail locked in the track.

FIG. 8 illustrates by this same view in section an inhibiting devicethat prevents voluntary or involuntary opening of the reverser.

Referring initially to FIG. 1, the thrust reverser 20 is essentially inthe form of a body of revolution about the axis 22 and surrounds aturbojet (not shown) of the “bypass” type, which is likewise centered onthe axis 22.

The reverser 20 is of the well-known cascade type. It comprises a fixedstructure 30 consisting of a front frame 32 and a rear frame indicatedby the reference 34 but not visible in FIG. 1, the front frame 32 andthe rear frame 34 being connected together by longitudinal members 36that are essentially parallel to the axis 22. The front frame 32 and therear frame 34 are each in the shape of a ring centered on the axis 22.The longitudinal members 36 have their front ends attached to the frontframe 32 and their rear ends attached to the rear frame 34. Together,the frames and longitudinal members form a squirrel cage supporting twocowlings 40. The first cowling 40 is on the inside toward the axis 22and guides the flow generated by the turbojet. The second cowling, whichcannot be seen in FIG. 1 because it is covered by the movable parts 50described later, is on the outside and guides the air flowing on theoutside of the reverser. FIG. 1 illustrates one type of reverser 20 thathas only two longitudinal members 36 that are on diametrically oppositesides with respect to the axis 22: the first longitudinal member 36 a,known as the “12 o'clock member” is toward the pylon of the airplane,i.e. usually above the reverser 20, and the second longitudinal member36 b referred to as the “6 o'clock member” is diametrically opposite thefirst with respect to the axis 22, i.e. usually at the bottom of thereverser. Notice that certain types of reverser do not have a rear frame34, but this does not affect the invention. Also notice that FIG. 1illustrates a reverser 20 divided into two half-shells assembled aroundthe turbojet, the “12 o'clock” longitudinal member 36 a and the “6o'clock” longitudinal member 36 b themselves therefore being dividedinto two in the length direction, but again this has no consequences onthe invention.

The fixed structure 30 thus comprises radial openings 38 that are eachdelimited in the forward direction by the front frame 32, in therearward direction by the rear frame 34 and separated from each other bythe longitudinal members 36.

For obvious reasons of stiffness and low weight, the components of thefixed structure 30 are hollow and made up of thin walls, such as sheetmetal or a composite material based on fiber or textile-reinforcedthermosetting resin. Such a fixed structure 30 is however still capableof being deformed under the impact of debris resulting from a vane orrotor of the turbojet braking.

Turning now to FIGS. 1 and 2, the reverser 20 also comprises movableparts 50 capable of covering the radial openings 38 by translatingforward in the closing direction 54, or uncovering them by an opposingrearward translation in the opening direction 52, these translationstaking place usually but not necessarily parallel to the axis 22. Noticethat in this example, which represents a common type of reverser, theopening direction 52 corresponds to a rearward or downstream movement ofthe reverser, while the closing direction 53 corresponds to a forward orupstream movement of the reverser. The reverser also has guide means 60consisting of rails 64 sliding in parallel tracks 62, the tracks 62being parallel to the axis 22 and attached to the longitudinal members36, for example on their flanks, and the rails 64 themselves beingattached to the movable parts 50. The reverser 20 also comprises controlmeans 70, usually in the form of screw actuators, attached to the frontframe 32 and parallel to the tracks 62: these actuators move the movableparts 50 in the opening 52 and closing 54 directions. Notice that thetracks 62 and the rails 64 are mechanical parts, sliding one inside theother with not much clearance. Thus, unlike the fixed structure 30, thetracks 62 and the rails 64 are more solid parts and less liable todeform. The tracks 62 and the rails 64 are usually of dovetail design.

When the movable parts 50 are covering the openings 38, they are held inthis “closed” position, as it is called, by locks attached to the fixedstructure 30. Usually, each movable part 50 is held by its front end bya “main” lock attached to the front frame 32. The main lock may howeverbecome inoperative in the event of deformation of the front frame 32following an impact. It is therefore usual to fit so-called back-uplocks on either side of each movable part 50, attaching them atdifferent locations than the main locks.

Referring now more particularly to FIG. 2, according to the inventionthe locking system 80 comprises locks 82 situated at the rear end 62 aof each track 62 in the opening direction 52, with each lock having abolt 110 positioned in line with the corresponding track 62, and thebolt 110 and therefore the lock 82 being in the vicinity of this rearend 62 a. The bolt 110 can be moved between a locked position and anopen position. When the rail 64 is retracted into the track 62, the bolt110 in the locked position prevents the rail 64 moving in the openingdirection 52, so that the bolt 110 keeps the rail 64 imprisoned in thetrack 62. In the open position, the bolt 110 no longer prevents suchmotion and the rail 64 can thus move in the opening direction 52. Thislocking system is therefore relatively insensitive to deformations ofthe fixed structure 30, even if these deformations are severe and affectthe ends 62 a of the tracks 62, because:

-   1. the bolt 110 remains lined up with the track 62 and thus    continues to perform its function, and-   2. the rail 64 is still imprisoned in the track 62: this keeps the    movable part 50 in its closed position over the corresponding radial    opening 38.

The lock 82 can be attached to the longitudinal member 36. It can alsobe attached, or indeed built in, directly to the end 62 a of the track62, thereby further reducing the risk of a relative movement occurringbetween the bolt 110 and the track 62. The important point is that thepath along which the load would be transferred between the end 62 a ofthe track and the point of attachment of the lock to the fixed structuremust be short.

In a first embodiment of the invention, the locks 82 are the main locks.

However, in a preferred embodiment of the invention, the locks 82 areback-up locks, the reverser having independent main locks, and possiblysecondary locks, based on known technology.

FIGS. 2 to 5 will now be considered. In this example, the locking system80 is used as a back-up. The locking system 80 comprises a lock 82 whichin turn comprises a body 90 attached to the longitudinal beam 36 in thevicinity of the end 62 a of the track. The body 90 in turn comprises atone end a U-shaped yoke 92, and this yoke 92 in turn comprises a base 94by which it is attached to the rest of the body 90 and two parallelwings 96 attached by one end to the base 94. The base 94 and the twowings 96 define an open space 98 which lies in the continuation of thetrack 62 and is therefore in the path of the rail 64. Consequently therail 64 passes between the two wings 96 when it moves in the openingdirection 52. The lock 82 also comprises a bolt 110 that moves between a“closed” position and an “open” position. When in the closed position,this bolt 110 prevents the rail 64 moving in the opening direction 52,i.e. the rail 84 stops against the bolt 110 when it is in the track 62and moving in the opening direction 52. When the bolt 110 is in the openposition, however, it does not prevent the rail 64 moving in the openingdirection. The example illustrated in the figures shows a cylindricalbolt 110 mounted so as to pivot, about an axis 112, in the wings 96,extending through the open space 98 between the two wings 96. One partof the bolt 110, situated between the wings 96, is in line with thetrack 62 and therefore in the path of the rail 64. The bolt 110 istherefore able to block the rail 64 when the latter is moving in theopening direction 52, as the end of the rail 64 situated in the openingdirection 52 stops against the bolt 110. The bolt 110 has a notch 118that allows the rail 64 to pass when the bolt is in the open position.When the bolt 110 is in the open position, the notch 118 is lined upwith the track 62 and the rail 64 can then move in the opening direction52, passing through the notch 118 without interfering with the bolt 110.When the bolt 110 has pivoted approximately 90° and reached the closedposition, the notch 118 is no longer lined up with the track 62. Thebolt 110 now prevents the rail 64 moving in the opening direction 52, sothe rail 64 is imprisoned in the track 62.

The locking system 80 also comprises bolt 110 control means 130. Thesecontrol means comprise firstly a lever 132 and an actuator 134. Thelever 132 is perpendicular to the bolt 110 and attached to itpreferably, but not necessarily, on the outside of the U yoke 92. Theactuator 134 is attached to the movable part 50 and preferably to therail 64 of the movable part 50. The actuator 134 is positioned so as toapply a force to the lever 132 when the rail 64 moves in the closingdirection 54 and reaches the end of its travel inside the track 62, thisforce causing the bolt 110 to pivot to the closed position. The controlmeans 130 also include a spring (not shown), such as a spiral spring,which applies a torque to the bolt 110 such as to pivot it automaticallyinto the open position. Lastly, the control means 130 comprise a catch(also not shown because hidden inside the body of the lock) that isitself controlled by a motor 138, the catch keeping the bolt 110automatically in the closed position despite the torque applied by thespring. In response to a signal the motor 138 allows the catch to bedisengaged in order to free the bolt 110 and allow it to pivot into theopen position under the action of the spring. The catch is of someordinary mechanical engineering design. It may take the form of, forexample, a pin sliding in the body 90 and pushed by a spring against thebolt 110, so that the pin passes into a hole in the bolt 110 when in thelocked position and so prevents the bolt 110 from pivoting, while themotor 138 can pull the pin out of the hole to release the bolt 110. Themotor 138 may for example be a linear electric motor with a core thatpasses into a solenoid, the moving core being connected to the rod orforming one end of this rod.

The movable parts of the reverser can thus be opened in the followingmanner:

-   -   A pulse is sent to the motors 138 to release the catches and        allow the springs to apply to the bolts 110 a torque capable of        pivoting them to the open position, complete pivoting not        however being able to occur at this level because the levers 132        stop against the actuators 134.    -   The movable parts 50, and by repercussion the actuators 134,        translate in the opening direction 52, freeing the levers 132        and allowing the springs to pivot the bolts 110 into the open        position. In this position the notches 118 are now lined up with        the tracks 62, allowing continued translation of the movable        parts 50 toward the rear 26 until the radial openings 38 are        completely free, as the rails 64 pass through the corresponding        notches 118.

The movable parts of the reverser can be closed in the following manner:

-   -   The movable parts 50, and by repercussion the actuators 134,        translate in the closing direction 54, the rails 64 retracting        fully into the tracks 62 and the movable parts 50 covering the        openings 38.    -   When the rails 64 reach the end of their travel and are no        longer in the notches 118, the actuators 134 push the levers 132        and cause the bolts 110 to rotate into the locked position as a        result of the translation in the closing direction 54 of the        movable parts 50 and of the associated actuators 134.    -   When the bolts reach the locked position, the catches 138 engage        automatically under the pressure of the springs, and the catches        then keep the bolts 110 automatically in this locked position.

It will be understood that the lock 82 may be in a “solid” form and belocated in a small space at the end of a track 62. This achieves twoadvantages for the invention:

-   -   It can be used on thin reversers, i.e. having little thickness.    -   The lock 82 can keep the rail 64 in the track 62 with a very        large force without generating large torques on the other parts        of the fixed structure. It can thus be held in position on this        fixed structure 30 simply by means of a lightweight component.

Another advantage of the invention is that the rail abuts endwiseagainst the bolt, so there is no torque on the rail.

Referring now to FIGS. 6, 7 and 8, if the airplane has to take off againbut a reverser is defective and it has not been possible to repair it,it is vital to neutralize this reverser visibly, and its movable partsmust remain in the closed position in a manner that can be relied upon.For this purpose the invention also provides an inhibiting device 150built into the locking system. This inhibiting device 150 comprises inthe U yoke 92 a bore 152 able to accommodate and retain an inhibitingrod 154, this bore 152 being positioned in such a way that theinhibiting rod 154, where present, prevents the rail 64 moving in theopening direction 52. The inhibiting rod 154 can be simply fitted byhand by the maintenance worker. Retention of the inhibiting rod 154 inthe bore 152 can be by any means. The inhibiting rod 154 is continued bya tail 156 of sufficient length to be able to pass through a hole 42 inthe cowling 40 and thus be visible from the outside, as shown in FIG. 8.In the example shown in FIG. 8, the tail 158 has a smaller diameter thanthe body 156 so as to form a shoulder which moves under gravity intocontact with another shoulder formed in the bore 152. During thepreflight inspection of the airplane, this tail 156 provides a visualcheck that reverser 20 operation is inhibited. The bore 152 ispreferably, but not necessarily, located between the bolt 110 and theend 64 a of the rail 64 when the latter is at the end of its travel inthe closing direction 54. It is thus possible to lock the movable parts50 in a position very close to the closed position.

1. A locking system on a cascade thrust reverser for a bypass turbojet,the reverser comprising a plurality of radial openings separated by oneor more longitudinal members, the radial openings being closed by one ormore movable parts moving in the closing direction, the radial openingsbeing exposed when the one or more movable parts move in the openingdirection, the reverser comprising guide means for the movable parts,the guide means comprising one or more rails attached to the movableparts and one or more tracks attached to a corresponding one of the oneor more longitudinal members, and the one or more rails sliding in theone or more tracks, characterized in that the locking system comprisesone or more locks located at an end of each of the one or more tracks inthe opening direction, each lock comprising a bolt positioned in linewith a corresponding track of the one or more tracks, the bolt beingmovable between a locked position and an open position, the bolt in thelocked position preventing a corresponding rail of the one or more railsfrom moving in the opening direction when the corresponding rail isretracted into the corresponding track, and the bolt in the openposition not preventing the corresponding rail from moving in theopening direction.
 2. The locking system as claimed in claim 1,characterized in that one of the one or more locks is attached to one ofthe longitudinal members.
 3. The locking system as claimed in claim 1,characterized in that one of the one or more locks is attached to theend of one of the one or more tracks.
 4. The locking system as claimedin claim 1, characterized in that the one or more locks are the mainlocks.
 5. The locking system as claimed in claim 1, characterized inthat the one or more locks are back-up locks.
 6. The locking system asclaimed in claim 5, characterized in that each of the one or more lockscomprises a body attached to a corresponding longitudinal member, thebody comprising a U-shaped yoke supporting a cylindrical pivoting bolt,that part of the bolt which is situated between the wings being in linewith a corresponding track and comprising a notch, said notch being inline with the corresponding track when the bolt is in the open position,said notch then allowing a corresponding rail to pass as it moves alongthe corresponding track, and the locking system also comprising controlmeans for operating the bolt between the locked position and the openposition.
 7. The locking system as claimed in claim 6, characterized inthat the control means comprise an actuator attached to the assemblyformed by the one or more movable parts and the one or more rails, alever attached to the bolt, a spring applying to the bolt a torquecapable of pivoting it into the open position, a catch thatautomatically immobilizes the bolt when in the locked position and amotor for releasing the catch in response to a signal, and the actuatorapplying a force to the lever when the rail moves in the closingdirection and reaches the end of its travel in the track, this forcehaving the effect of pivoting the bolt into the closed position.
 8. Thelocking system as claimed in claim 6, characterized in that the lockingsystem comprises a bore and an inhibiting rod, this bore being locatedin the U-shaped yoke, the bore being positioned in such a way that theinhibiting rod, when present in the bore, prevents the rail moving inthe opening direction.
 9. The locking system as claimed in claim 8, theinhibiting rod being present in the bore, characterized in that theinhibiting rod is continued by a tail of sufficient length to be able topass through a hole in the cowling and thus be visible on the outside.10. The locking system as claimed in claim 2, characterized in that thelocks are the main locks.
 11. The locking system as claimed in claim 3,characterized in that the locks are the main locks.
 12. The lockingsystem as claimed in claim 2, characterized in that the locks areback-up locks.
 13. The locking system as claimed in claim 3,characterized in that the locks are back-up locks.
 14. The lockingsystem as claimed in claim 7, characterized in that the locking systemcomprises a bore and an inhibiting rod, this bore being located in theU-shaped yoke, the bore being positioned in such a way that theinhibiting rod, when present in the bore, prevents the rail moving inthe opening direction.